1. Field of the Invention
This invention relates to the field of water based epoxy resins. It particularly relates to modified glycidyl ethers of bisphenol A type resins which are useful as coatings.
2. Prior Art
Water based epoxy resins are known in the art. Prior art water based epoxy resins generally utilize an emulsifier and an organic solvent in their formulation. The presence of organic solvent provides a problem because of volatile solvent release. Therefore, those skilled in the art have sought to provide a water based epoxy resin which is free of the difficulties inherent in using large amounts of organic solvents. In U.S. Pat. No. 3,998,771 a process is disclosed whereby a carboxylic acid is reacted with a primary amine to form an amide. This amide is then reacted in excess with an epoxy resin and the product is water dispersed and further reacted with enough epoxy resin to stoichiometrically cure the resin.
Emulsification of water based epoxy resins is not without its difficulties. Emulsification of the polar epoxy resins with surfactants or emulsifying agents is in fact generally quite difficult. All surfactants or emulsifiers promote hydrolysis of epoxy groups in water systems. This generally leads to poor emulsification stability, poor freeze-thaw stability, usually a phase inversion with addition of curing agent and poor pigment stability. Surfactants and emulsifiers, if added to an epoxy system, usually become incompatible after curing and exude to the coating surface forming blemishes or blushed coatings.
A water reducible coating system is described in U.S. Pat. No. 4,167,498 which is prepared by combining a bisphenol A epoxy resin with a polyamide prepared from fatty acids and an amino propyl derivative of a polyoxyalkylene polyamine.
U.S. Pat. No. 4,308,183 describes a water borne coating employing a bisphenol A epoxy resin produced by addition of an ethoxylated nonylphenol and a long chain organic phosphatide.
U.S. Pat. No. 4,315,044 describes a self-emulsifying epoxy resin employing the diglycidyl ether of bisphenol A, bisphenol A and the diglycidyl ether of polyoxyalkylene glycol in aqueous medium.
It is well known in the art that there is a need for water reduced coating systems which minimize the use of hazardous or polluting solvents and produce high gloss clear and pigmented coatings.